This invention relates to force flow valve type multi-ply walled shipping bags which include in the bag wall an intermediate ply which is a vapor barrier, and particularly to such a bag having a sealable vent by passing the vapor barrier ply.
Force flow packaging with valve bags to increase flow rate and powder compaction is difficult, if not impractical to accomplish, due to the air release problem when the bag contains a vapor barrier.
Needle hole perforations in the vapor barrier have been used to alleviate the problem, but their presence destroys the integrity of the vapor barrier.
Without air relief from powder fill through the sides and bottom of the bag, compaction of the bag contents cannot be effected and the bag filling rate is impractically slow and cumbersome.